This invention relates to a ring derrick having a stationary counterweight.
Cranes and derricks lift heavy loads at varying radii from the base of the lifting boom. The value of the load times radius—load moment—is an important measure of lifting capacity. The world's largest crawler cranes have maximum load moments of about 32,000 metric tonne-meters (Manitowoc 31000), 44,000 tonne-meters (Terex Demag CC8800 Twin), 50,000 tonne-meter range (new Liebherr XXL not yet released), and 80,000 tonne-meters (Lampson LTL2600). These maximum load moments typically occur at minimum operating radius with the heaviest lifted load.
It would be desirable to achieve substantially greater load moment capacity, at much greater operating radii.
Typical mobile crawler cranes may produce ground bearing pressures of 20,000 psi. Such pressures normally require a pile-supported foundation system. It would be better to substantially reduce bearing pressures and thus avoid the need for a pile supported foundation.
Maximum operating wind speeds for cranes identified above are in the 18 mph range. Low wind tolerance can cause considerable down time, which leads to schedule problems for a major construction project. Substantial improvements in wind tolerance would substantially improve productivity in windy locations.
All existing construction crawler cranes carry their counterweights. That arrangement increases ground bearing pressure, which adversely affects the machine's stability and ultimately its safety. Eliminating this problem is a primary goal of the present invention.